Coronavirus Antibody Testing and Immunity Passports
The WHO put out a statement recently about how antibody testing cannot be used for “immunity passports” because the test cannot guarantee immunity. This raised a lot of anxiety and questions. There are a few things to understand from a science perspective.
An “immunity passport” may inadvertently incentivize disease spread. — Wei-Shin Lai, M.D.
- SARS antibodies lasted about 3 years. SARS and MERS are coronavirus diseases most similar to COVID-19. People who contracted these diseases produced antibodies that lasted for about three years. Although not a guarantee against illness, having antibodies means that your body still has immune cells that can recognize the virus and ramp up very quickly to fight it. When your immune system forgets the virus, your antibody levels decrease. It will take longer to mount a defense, so you will exhibit worse illness if you catch the virus.
- Cold-causing coronavirus antibodies may only last for months. Some coronvaviruses also cause the common cold. The length of time for those antibodies is actually just months, so you could catch the same coronavirus cold over and over again. The current novel coronavirus is genetically closer to SARS than the cold-causing coronaviruses. Hopefully the immunity response is closer to SARS as well, lasting 2–3 years rather than just months.
- There is cross reaction between coronaviruses. The antibody test is not very specific for SARS-CoV-2, the virus that causes COVID-19. Other coronaviruses may crossreact and result in a positive test. So if you recently had a common cold coronavirus, you may test positive even though you never had COVID-19 and are not immune to it. There are over a dozen tests now available in the US, and some are better than others.
- 1/3 of recovered people don’t produce a strong antibody response. Your body has various types of immunity responses. About a third of people’s defense against this virus is less dependent on the antibody response, so their antibody levels remain very low even after recovering from the disease. For those people, it is unclear how immune they are, even if the test shows up positive. (For those of you interested in the science, what’s relevant here is cellular immunity versus humoral immunity. T-cells from the thymus may play a large role in COVID-19, which may explain why kids don’t have bad disease compared with older people who no longer have a functioning thymus.)
- The test has a high false positive rate. Some tests are better than others. If a test has a false positive rate of 5%, that means that for every 1000 people tested, 50 will have a false positive. Imagine that a grocery store chain tests all 1000 of their workers. 50 of them will show up positive, even if they never had the disease. These 50 people may believe that they can’t catch the disease again and go back to work. But then they end up catching the disease, being symptomatic, and spread the virus to other people. This is the problem with allowing an “immunity passport” using just this test.
- The test may cause complacency. Even if a young healthcare worker has recovered from COVID-19, has a high antibody titer, and is very unlikely to get sick again in the next few years, they still have to exercise all precautions as if they were not immune. If they come into contact with a patient who has the virus, they could get the virus on their clothing, their hands, or their face. If they take care of another patient without properly decontaminating, they could spread the virus to that patient. The reason a surgeon wears a mask when operating is more to protect the patient from the surgeon rather than to protect the surgeon from the patient. A recovered person still has to take all precautions.
The concept of an immunity passport is fraught with politics, problematic application of bad science, and bribery. In an attempt to “save the economy,” some people may deliberately seek infection to acquire this “passport” sooner. There should be no reward for catching this virus. The existance of such a “golden ticket” for travel, meeting with clients, and the ability to make more money than collecting unemployment means that some people will try to get sick sooner so they can return to normal activities. Similar to chickenpox lollipop parties, there could be COVID-19 dinner parties for a ticket price of $200. When so few people have had the illness, and an immunity passport could inadvertently incentivize disease spread.
An immunity passport is not the answer for re-opening the economy right now. It has been and remains testing, tracing, and quarantine. With that, most businesses can restart. And everyone has to continue some minimum social distancing until the vaccine.
Wei-Shin Lai M.D. is the co-founder and CEO of AcousticSheep LLC, makers of SleepPhones® headphones, the most comfortable headphones you can wear in bed. She was once offered a job with the CDC as an epidemic intelligence officer.
